`There are many theories to explain why fashion editors go...

WRITING FROM LONDON — `There are many theories to explain why fashion editors go mad,``

according to Nicholas Coleridge, a brash young Britisher who knows enough of them to populate several good-sized asylums.

But fashion editors, those international brokers of style, are hardly alone in their dementia. In fact, of the 400 designers, manufacturers, buyers, workers, customers and journalists from 14 countries interviewed for his new book, ``The Fashion Conspiracy`` (Harper & Row, $19.95), Coleridge says,

``only about 50 seemed altogether sane.``

Two years after being named editor of Harpers & Queen, one of Britain`s leading fashion and lifestyle magazines, Coleridge himself is unsure as to whether he`s fallen prey to madness a la mode. ``What mad person knows they`re mad?`` he muses, nursing a glass of wine beside the fire in his cozy Chelsea home, a duplex decorated with rugs and wall hangings from travels in India.

Even worse, perhaps he has finally become one of ``them,`` a fashion creature. ``No, well, only a bit,`` he says, with a nervous giggle.

``If I know that a month of fashion collections is coming up, I try to make a point, for the two weeks before, to see as many people as I can who have absolutely nothing to do with fashion. I think it`s jolly important to see all kinds of people who have actually never heard the two words `Christian Lacroix.` I think it`s highly good for your sanity to be with people who think `Chanel` is the strip of water between England and France,`` he says firmly, then grins, clearly pleased at the pun.

COMING RIGHT UP

At 30, dapper and gracefully balding, Coleridge is one of British publishing`s boy wonders. Having had his first article published in Harpers & Queen when he was a 15-year-old schoolboy at Eton, he went on to the cheeky Tatler magazine after graduating from Cambridge University. A columnist for the London Evening Standard before joining Harpers & Queen as features editor three years ago, he also is the author of a travel book and a novel.

Charming in manner and vicious in wit, Coleridge combines a travel writer`s flair for atmosphere, a gossip writer`s ear for the carelessly spoken word and a reporter`s deadpan recitation of the facts to devastating effect in ``The Fashion Conspiracy.``

From the sweatshops of Korea to the perfumed boudoirs of Paris, in all its bitchery and bravura, Coleridge explores the modern ``spice route`` of international style, producing an informative and entertaining, if

frightening, primer on the fashion world and its denizens.

``World`` is the operative word here. Like a stellar burst of energy that has whirled faster and faster, turning in upon itself in recent years, fashion has gone nova, creating a universe unto itself. Replete with its own versions of culture, customs, language, ambassadors, foreign intelligence services, protocol and power structures, he says, ``it`s a complete country apart.``

IT`S A SMALL WORLD

Populated by people who see less of their friends than they do of one another, crossing paths regularly in the same showrooms, press centers, hotels and airports in Milan, London, Paris, New York and Rome, the fashion world has developed a case of raging xenophobia, Coleridge claims.

``It`s really like `Fashion Land.` And, once you`ve been sucked into it, it`s extremely compelling-and I can`t see any particular reason for people to wander out of it.``

They tend to wander even deeper into it. That`s where fashion madness begins. ``There is that extraordinary danger, which I think particularly strikes unmarried fashion editors and unmarried store buyers, of losing complete sense of proportion over things like where they sit at a fashion show,`` Coleridge says, sighing at the pathos.

``I make it a point now of always offering my seat to anybody else who looks like they want it more, because I really could not care less.`` Clearly not cut out for the hardscrabble maneuverings of those whose self-esteem rides on a row number, it is easy to believe Coleridge, who usually but not always gets front-row treatment.

``It`s that sense of proportion that everything in fashion conspires to make you lose. And you see it, again and again, in the way things are described,`` he continues. ``I`m talking here of the less intelligent end of people doing this sort of thing: the mad lurches, based on instinct, when something is suddenly regarded as not being good-in fact, as being downright awful. When, in fact, it usually simply means that one designer has done just slightly better that season or has come out with some interesting thing.

``I suppose it has something to do with getting the clothes and being in the right restaurants and things. People do terrifically dislike the idea that they`re not in fashion. I suppose that`s why it`s fashion.``